Various types of instrument panels are known in the prior art which have at least one aperture therein for receiving an instrument such as an aircraft instrument. For viewing the instruments at night, prior art panels have included a section formed of light transmitting material, a light source coupled to the section and opaque coverings on the inner and outer surfaces of the light transmitting section for causing transmission of light from the light source only in the plane of the panel. The area of the light transmitting section of the panel which immediately surrounds the instrument illuminates the face of the instrument in the aperture. However, this light transmitted from the area surrounding the aperture, and illuminating the face of the instrument, is directly visible to the observer and, thus, detracts from the observation of the instrument itself.
In order to overcome this disadvantage, prior art panels have the light transmitting area immediately surrounding the aperture beveled or sloped at an angle in order to reduce the direct transmission of the emitted light in the direction of the front of the panel.
In some cases in the prior art, a shield is placed on the panel surrounding the aperture in such a manner as to attempt to partially cover the beveled edges to reduce the amount of emitted light being transmitted directly to the front of the panel.
However, these prior art devices have not been entirely satisfactory inasmuch as a large amount of the emitted light is not blocked and is transmitted directly toward the front of the panel where it can be seen by the observer.
The present invention overcomes these disadvantages by providing an instrument panel of the type being integrally formed of light transmitting material and which is designed such that direct transmission of the emitted light in the direction of the front of the panel is minimized. This is accomplished by providing each aperture with a cylindrical portion extending partially into the front of the panel and beveled edges on at least a portion of the remainder of the aperture toward the object for emitting light and illuminating the object. The angle of the beveled edge and the depth of the cylindrical portion are selected such that direct transmission of the emitted light toward the front of the panel is minimized.
In one embodiment, the beveled edges of the aperture form a frusto-conical surface with the small diameter intersecting and in mating alignment with the cylindrical portion of the aperture which extends into the panel from the front.
In another embodiment, perpendicular sides on the aperture extend partially into the front of the panel toward the object to be viewed with beveled edges on at least a portion of the remainder of the aperture toward the object for emitting light and illuminating the object, the angle of the beveled edges and the length of the perpendicular sides being selected such that direct transmission of the emitted light in the direction of the front of the panel is minimized.
An important feature of the invention is the ratio of the length of the perpendicular sides of the aperture to the angle of the beveled edges which ratio varies with the thickness of the panel.
The invention also includes at least one frusto-conical shaped aperture in a supporting plate integrally formed of light transmitting material. The small diameter of the frusto-conical shaped aperture is at the front of the plate and the large diameter is at the back of the plate in the direction of the object to be illuminated to form a beveled surface for emitting light to illuminate the object. An opaque plate is mounted on the front of the light transmitting plate to cause light to be emitted only from the beveled surfaces, and a cylindrical aperture in the opaque plate is in mating alignment with the small diameter of the frusto-conical aperture to enable the object to be viewed while minimizing direct transmission of the emitted light toward the front of the panel.